THE ANDALITES
The Andalite's are one of the most superior races, when it comes to technology and fighting. They have faster than light ship, and many of them. They have battle trained warriors and they look dangerous with their sharp scorpion shaped tails and are dangerous with their fast and accurate swipes and weapons, shredders and Dracon beams. Also the ability to change into any creature they wish as long as they have they creatures DNA (this is known as morphing). Because of all this the Andalite's are basically the most superior race across the galaxy.
Andalite's are the reason that Yeerks can move around the galaxy.
A long time ago a Prince, Prince Seerow, visited the Yeerk homeland. At this time Yeerks were only slugs in pools soaking up Kandrona rays, apart from a few lucky ones who had Gedds (the other species on their planet) as hosts. Gedds weren't much of a host as they were almost blind and deaf and fairly clumsy. Now Prince Seerow felt sorry for the Yeerks as they couldn't explore the galaxy or even get off their planet. He also felt sorry for the Yeerks as they seemed like a fairly intelligent species but couldn't do anything as the Gedds were limited in what they could do. So Prince Seerow gave them faster than light ships so they could travel around space. This was a big mistake. The Yeerks began to crave other hosts and with the Andalite's ships and the Andalite's weapons they began taking over other species. First there was the Gedds from their own planet, then the Taxxons and then the Hork-Bajir. All this time the Andalites were following the Yeerks fighting them as they felt it their duty. The Yeerks took over many species but they could never defeat the Andalites. Only one Andalite was ever made a host, War Prince Alloran-Semitur-Corrass whose Yeerk quickly became Visser 3 and then near the end of the war he became Visser 1. The Yeerks target after Taxxons became humans, because of the fact that there was millions of them. Unfortunately the Andalite's were unable to reach Earth for 3 years so Earth was left to their own devices and when the Andalite's did reach Earth, the Yeerks were defeated.
After the war their became a friendship between the Andalites and humans. Andalites would come back and forth between Earth. The Andalites didn't have a mouth in their natural form so they would come to Earth, acquire a human morph then race off to a shop for chocolate, cinnamon buns or jelly beans which were Andalites favourite human food (that and cigarette butts). Some Andalites lived on Earth in their space craft or they could make a Andalite house, a scoop. Andalites also allowed morphing cubes be available to certain people to prevent terrorism attacks.
Andalites are (or can be) ruthless and arrogant but are also a peaceful species.
Here is a pic of one (Prince Elfangor-Sirinial-Shamtul to be exact)
As you can see they have a human head (minus the mouth and plus the eyestalks) and torso with legs like a horse and a scorpion tail covered in blue fur. They speak through thought-speak which is were you 'talk' by thinking your thoughts. Thought-speak works two ways: For everyone to hear or private thought-speak. For everyone to hear you direct your thoughts to everyone. For private thought-speak you direct your thoughts to only one person.